So-called online games have become popular, wherein a game server provides game data to clients via a network and the clients perform game functions based on the provided game data. In an online card game, which is a sort of online game, a player is provided with game contents such as character cards and items used in the game. An example of such a card game is disclosed in Japanese Patent Application Publication No. 2009-187143. Also, a method of selecting a game content to be provided to a player is disclosed in Japanese Patent Application Publication No. 2008-93165 (the “'165 Publication”). In the game disclosed in the '165 Publication, each game content is associated with a winning probability and one or more game contents to be provided to a player are selected based on the winning probability in response to an acquisition request (purchase request) for one or more game contents from the player.
Cards with low winning probabilities are sometimes called “rare cards.” Many games are designed such that rare cards can be used to progress the games advantageously. Therefore, many players seek rare cards in the games. In many cases, players have to make a multiple of acquisition requests (or lottery requests) for game contents before obtaining rare cards with low winning probabilities.
In many on-line card games, an acquisition request for a game content can be made at the expense of in-game points. Therefore, as the more acquisition requests are made to acquire a rare card, the more costs such as in-game points are consumed before obtaining a desired rare card. Since a game content to be provided to a player is selected from a certain population based on winning probabilities, the number of acquisition requests required to obtain a rare card can be known based only on stochastic prediction by a player. The actual costs required does not necessarily agree with stochastic prediction (player's expectation). Rather, in many cases, the actual cost deviates from the expected value to some extent. Thus, where a game content to be provided to a player is selected from a certain population based on winning probabilities, players cannot make an accurate prediction of costs required to obtain a desired game content.